Arguments

There are two argument sections; together they comprise one-half
of the LSAT. Each section is 35 minutes long and contains roughly
24 questions. This section is not as highly "timed" as the games,
so it is reasonable to set as your goal the completion of the entire
section. Unlike with games, determining the level of difficulty
of an argument is itself difficult, so just start with the first
question and then work through the section.

INTRODUCTION

An argument, as used on the LSAT, is a presentation of facts and
opinions in order to support a position. Many arguments will be
fallacious. And many correct answers will be false! This often causes
students much consternation; they feel that the correct answer should
be true. But the arguments are intended to test your ability to
think logically. Now logic is the study of the relationships between
statements, not of the truth of those statements. Being overly concerned
with finding the truth can be ruinous to your LSAT logic score.

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"2 OUT OF 5" RULE

Creating a good but incorrect answer-choice is much harder than
developing the correct answer. For this reason, usually only one
attractive wrong answer-choice is presented. This is called the
"2 out of 5" rule. That is, only two of the five answer-choices
will have any real merit. Hence, even if you don't fully understand
an argument, you probably can still eliminate the three fluff choices,
thereby greatly increasing your odds of answering the question correctly.

LOGIC I

Although in theory the questions on the LSAT argument section are
designed to be answered without any reference to formal logic, the
section is essentially a logic test. Some knowledge of the fundamentals
of logic, therefore, will give you a definite advantage. Armed with
this knowledge, you should quickly notice that the arguments are
fundamentally easy and that most of them fall into a few basic categories.
In this section, we will study the logical structure of arguments.
In Logic II, we will symbolize and diagram arguments in much the
same way as we did with games.

Conclusions

Most argument questions hinge, either directly or indirectly, on
determining the conclusion of the argument. The conclusion is the
main idea of the argument. It is what the writer tries to persuade
the reader to believe. Most often the conclusion comes at the end
of the argument. The writer organizes the facts and his opinions
so that they build up to the conclusion. Sometimes, however, the
conclusion will come at the beginning of an argument, rarely does
it come in the middle, and occasionally, for rhetorical effect,
the conclusion is not even stated.

Example:

The police are the armed guardians of the social order. The blacks
are the chief domestic victims of the American social order. A
conflict of interest exists, therefore, between the blacks and the
police.--Eldridge Cleaver, Soul on Ice

Here the first two sentences anticipate or set up the conclusion.
By changing the grammar slightly, the conclusion can be placed at
the beginning of the argument and still sound natural:

A conflict of interest exists between the blacks and the police
because the police are the armed guardians of the social order
and the blacks are the chief domestic victims of the American social
order.

The conclusion can also be forced into the middle:

The police are the armed guardians of the social order. So a
conflict of interest exists between the blacks and the police
because the blacks are the chief domestic victims of the American
social order.

It is generally awkward, as in the previous paragraph, to place
the conclusion in the middle of the argument because then it cannot
be fully anticipated by what comes before nor fully explained by
what comes after. On the rare occasion when a conclusion comes in
the middle of an argument, most often either the material that comes
after it or the material that comes before it is not essential.

In summary: To find the conclusion, check the last sentence
of the argument. If that is not the conclusion, check the first
sentence. Rarely does the conclusion come in the middle of an argument.

When determining the meaning of a conclusion, be careful not to
read any more into it than what the author states. Although arguments
are not worded as precisely as games, you still need to read them
with more care than you would use in your everyday reading.

As with games, read the words and sentences of an argument precisely,
and use their literal meaning.

For example, consider the meaning of some in the sentence "Some
of Mary's friends went to the party." It would be unwarranted, based
on this statement, to assume that some of Mary's friends did not
go to the party. Although it may seem deceiving to say that some
of Mary's friends went to the party when in fact all of them did,
it is nonetheless technically consistent with the meaning of some.

Some means "at least one and perhaps all."

As mentioned before, the conclusion usually comes at the end of
an argument, sometimes at the beginning, and rarely in the middle.
Writers use certain words to indicate that the conclusion is about
to be stated. Following is a list of the most common conclusion
indicators:

Conclusion Indicators

hence

therefore

so

accordingly

thus

consequently

follows that

shows that

conclude that

implies

as a result

means that

Most often the conclusion of an argument is put in the form of
a statement. Sometimes, however, the conclusion is given as a command
or obligation.

Example:

All things considered, you ought to vote.

Here, the author implies that you are obliged to vote.

The conclusion can even be put in the form of a question. This
rhetorical technique is quite effective in convincing people that
a certain position is correct. We are more likely to believe something
if we feel that we concluded it on our own, or at least if we feel
that we were not told to believe it. A conclusion put in question
form can have this result.

Example:

The Nanuuts believe that they should not take from Nature anything
She cannot replenish during their lifetime. This assures that future
generations can enjoy the same riches of Nature that they have.
At the current rate of destruction, the rain forests will disappear
during our lifetime. Do we have an obligation to future generations
to prevent this result?

Here the author trusts that the power of her argument will persuade
the reader to answer the question affirmatively.

Taking this rhetorical technique one step further, the writer may
build up to the conclusion but leave it unstated. This allows the
reader to make up his own mind. If the build-up is done skillfully,
the reader will be more likely to agree with the author, without
feeling manipulated.

Example:

He who is without sin should cast the first stone. There is no
one here who does not have a skeleton in his closet.

The unstated but obvious conclusion here is that none of the people
has the right to cast the first stone.

When determining the conclusion's scope be careful not to read
any more or less into it than the author states. LSAT writers often
create wrong answer-choices by slightly overstating or understating
the author's claim. Certain words limit the scope of a statement.
These words are called quantifiers--pay close attention to them.
Following is a list of the most important quantifiers:

Quantifiers

all

except

likely

some

most

many

only

could

no

never

always

everywhere

probably

must

alone

Example:

Whether the world is Euclidean or non-Euclidean is still an open
question. However, if a star's position is predicted based on non-Euclidean
geometry, then when a telescope is pointed to where the star should
be it will be there. Whereas, if the star's position is predicted
based on Euclidean geometry, then when a telescope is pointed to
where the star should be it won't be there. This strongly indicates
that the world is non-Euclidean.

Which one of the following best expresses the main idea of the
passage?

(A) The world may or may not be Euclidean.
(B) The world is probably non-Euclidean.
(C) The world is non-Euclidean.
(D) The world is Euclidean.
(E) The world is neither Euclidean nor non-Euclidean.

Choice (A) understates the main idea. Although the opening to the
passage states that we don't know whether the world is non-Euclidean,
the author goes on to give evidence that it is non-Euclidean. Choice
(C) overstates the main idea. The author doesn't say that the world
is non-Euclidean, just that evidence strongly indicates that it
is. In choice (B), the word "probably" properly limits the scope
of the main idea, namely, that the world is probably non-Euclidean,
but we can't yet state so definitively. The answer is (B).

Premises

Once you've found the conclusion, most often everything else in
the argument will be either premises or "noise." The premises provide
evidence for the conclusion; they form the foundation or infrastructure
upon which the conclusion depends. To determine whether a statement
is a premise, ask yourself whether it supports the conclusion. If
so, it's a premise. Earlier we saw that writers use certain words
to flag conclusions; likewise writers use certain words to flag
premises. Following is a partial list of the most common premise
indicators:

Premise Indicators

because

for

since

is evidence that

if

in that

as

owing to

suppose

inasmuch as

assume

may be derived from

Example:

Since the incumbent's views are out of step with public opinion,
he probably will not be reelected.

Here "since" is used to flag the premise that the incumbent's positions
are unpopular.

Suppressed Premises

Most arguments depend on one or more unstated premises. Sometimes
this indicates a weakness in the argument, an oversight by the writer.
More often, however, certain premises are left tacit because they
are too numerous, or the writer assumes that his audience is aware
of the assumptions, or he wants the audience to fill in the premise
themselves and therefore be more likely to believe the conclusion.

Example:

Conclusion: I knew he did it.

Premise: Only a guilty person would accept immunity from prosecution.

The suppressed premise is that he did, in fact, accept immunity.
The speaker assumes that his audience is aware of this fact or at
least is willing to believe it, so to state it would be redundant
and ponderous. If the unstated premise were false (that is, he did
not accept immunity), the argument would not technically be a lie;
but it would be very deceptive. The unscrupulous writer may use
this ploy if he thinks that he can get away with it. That is, his
argument has the intended effect and the false premise, though implicit,
is hard to find or is ambiguous. Politicians are not at all above
using this tactic.

A common question on the LSAT asks you to find the suppressed premise
of an argument. Finding the suppressed premise, or assumption, of
an argument can be difficult. However, on the LSAT you have an advantage--the
suppressed premise is listed as one of the five answer-choices.
To test whether an answer-choice is a suppressed premise, ask yourself
whether it would make the argument more plausible. If so, then it
is very likely a suppressed premise.

Example:

American attitudes tend to be rather insular, but there is much
we can learn from other countries. In Japan, for example, workers
set aside some time each day to exercise, and many corporations
provide elaborate exercise facilities for their employees. Few American
corporations have such exercise programs. Studies have shown that
the Japanese worker is more productive than the American worker.
Thus it must be concluded that the productivity of American workers
will lag behind their Japanese counterparts, until mandatory exercise
programs are introduced.

The conclusion of the argument is valid if which one of the following
is assumed?
(A) Even if exercise programs do not increase productivity, they
will improve the American worker's health.
(B) The productivity of all workers can be increased by exercise.
(C) Exercise is an essential factor in the Japanese worker's superior
productivity.
(D) American workers can adapt to the longer Japanese work week.
(E) American corporations don't have the funds to build elaborate
exercise facilities.

The unstated essence of the argument is that exercise is an integral
part of productivity and that Japanese workers are more productive
than American workers because they exercise more. The answer is
(C).

Counter-Premises

When presenting a position, you obviously don't want to argue against
yourself. However, it is often effective to concede certain minor
points that weaken your argument. This shows that you are open-minded
and that your ideas are well considered. It also disarms potential
arguments against your position. For instance, in arguing for a
strong, aggressive police department, you may concede that in the
past the police have at times acted too aggressively. Of course,
you will then need to state more convincing reasons to support your
position.

Example:

I submit that the strikers should accept the management's offer.
Admittedly, it is less than what was demanded. But it does resolve
the main grievance--inadequate health care. Furthermore, an independent
study shows that a wage increase greater than 5% would leave the
company unable to compete against Japan and Germany, forcing it
into bankruptcy.

The conclusion, "the strikers should accept the management's offer,"
is stated in the first sentence. Then "Admittedly" introduces a
concession; namely, that the offer was less than what was demanded.
This weakens the speaker's case, but it addresses a potential criticism
of his position before it can be made. The last two sentences of
the argument present more compelling reasons to accept the offer
and form the gist of the argument.

Following are some of the most common counter-premise indicators:

Counter-Premise Indicators

but

despite

admittedly

except

even though

nonetheless

nevertheless

although

however

in spite of the fact

As you may have anticipated, the LSAT writers sometimes use counter-premises
to bait wrong answer-choices. Answer-choices that refer to counter-premises
are very tempting because they refer directly to the passage and
they are in part true. But you must ask yourself "Is this the main
point that the author is trying to make?" It may merely be a minor
concession.

Logic II (Diagramming)

We thoroughly covered diagramming in the game section. Diagramming
is also useful with arguments. However, the diagrams won't be as
elaborate as those used with games. In fact, in these cases, the
term "diagramming " is somewhat of a misnomer. Rarely will we actually
draw a diagram; instead we will symbolize the arguments, much as
we did the conditions of the games.

Most arguments are based on some variation of an if-then
statement. However, the if-then statement is often embedded
in other equivalent structures. We already studied embedded if-then
statements in the chapter on flow charts. Still, we need to further
develop the ability to recognize these structures.

If-ThenA-->B

By now you should be well aware that if the premise of an if-then
statement is true then the conclusion must be true as well. This
is the defining characteristic of a conditional statement; it can
be illustrated as follows:

A-->BATherefore, B

This diagram displays the if-then statement "A-->B," the
affirmed premise "A," and the necessary conclusion "B." Such a diagram
can be very helpful in showing the logical structure of an argument.

Example: (If-then)

If Jane does not study for the LSAT, then she will not score well.
Jane, in fact, did not study for the LSAT; therefore she scored
poorly on the test.

When symbolizing games, we let a letter stand for an element. When
symbolizing arguments, however, we may let a letter stand for an
element, a phrase, a clause, or even an entire sentence. The clause
"Jane does not study for the LSAT" can be symbolized as ~S, and
the clause "she will not score well" can be symbolized as ~W. Substituting
these symbols into the argument yields the following diagram:

~S-->~W~STherefore, ~W

This diagram shows that the argument has a valid if-then
structure. A conditional statement is presented, ~S-->~W; its premise
affirmed, ~S; and then the conclusion that necessarily follows,
~W, is stated.

Embedded If-Then Statements

Usually, arguments involve an if-then statement. Unfortunately,
the if-then thought is often embedded in other equivalent
structures. In this section, we study how to spot these structures.

Example: (Embedded If-then)

John and Ken cannot both go to the party.

At first glance, this sentence does not appear to contain an if-then
statement. But it essentially says: "if John goes to the party,
then Ken does not."

Example: (Embedded If-then)

Danielle will be accepted to graduate school only if she does well
on the GRE.

Given this statement, we know that if Danielle is accepted to graduate
school, then she must have done well on the GRE. Note: Students
often wrongly interpret this statement to mean:

"If Danielle does well on the GRE, then she will be accepted to
graduate school."

There is no such guarantee. The only guarantee is that if she does
not do well on the GRE, then she will not be accepted to graduate
school.

"A only if B" is logically equivalent to "if A, then B."

Affirming the Conclusion Fallacy

A-->BBTherefore, A

Remember that an if-then statement, A-->B, tells
us only two things: (1) If A is true, then B is true as well. (2)
If B is false, then A is false as well (contrapositive). If, however,
we know the conclusion is true, the if-then statement tells
us nothing about the premise. And if we know that the premise is
false (we will consider this next), then the if-then statement
tells us nothing about the conclusion.

Example: (Affirming the Conclusion Fallacy)

If he is innocent, then when we hold him under water for sixty
seconds he will not drown. Since he did not die when we dunked him
in the water, he must be innocent.

The logical structure of the argument above is most similar to
which one of the following?

(A) To insure that the remaining wetlands survive, they must be
protected by the government. This particular wetland is being neglected.
Therefore, it will soon perish.
(B) There were nuts in that pie I just ate. There had to be, because
when I eat nuts I break out in hives, and I just noticed a blemish
on my hand.
(C) The president will be reelected unless a third candidate enters
the race. A third candidate has entered the race, so the president
will not be reelected.
(D) Every time Melinda has submitted her book for publication it
has been rejected. So she should not bother with another rewrite.
(E) When the government loses the power to tax one area of the economy,
it just taxes another. The Supreme Court just overturned the sales
tax, so we can expect an increase in the income tax.

To symbolize this argument, let the clause "he is innocent" be
denoted by I, and let the clause "when we hold him under water for
sixty seconds he will not drown" be denoted by ~D. Then the argument
can be symbolized as

I-->~D~DTherefore, I

Notice that this argument is fallacious: the conclusion "he is
innocent" is also a premise of the argument. Hence the argument
is circular--it proves what was already assumed. The argument affirms
the conclusion then invalidly uses it to deduce the premise. The
answer will likewise be fallacious.

We start with answer-choice (A). The sentence

"To insure that the remaining wetlands survive, they must be protected
by the government"

contains an embedded if-then statement:

"If the remaining wetlands are to survive, then they must be protected
by the government."

This can be symbolized as S-->P. Next, the sentence "This particular
wetland is being neglected" can be symbolized as ~P. Finally, the
sentence "It will soon perish" can be symbolized as ~S. Using these
symbols to translate the argument gives the following diagram:

S-->P~PTherefore, ~S

The diagram clearly shows that this argument does not have the
same structure as the given argument. In fact, it is a valid argument
by contraposition.

Turning to (B), we reword the statement "when I eat nuts, I break
out in hives" as

"If I eat nuts, then I break out in hives." This in turn can be
symbolized as N-->H.

Next, we interpret the clause "there is a blemish on my hand" to
mean "hives," which we symbolize as H. Substituting these symbols
into the argument yields the following diagram:

N-->HHTherefore, N

The diagram clearly shows that this argument has the same structure
as the given argument. The answer, therefore, is (B).

Denying the Premise Fallacy

A-->B~ATherefore, ~B

The fallacy of denying the premise occurs when an if-then
statement is presented, its premise denied, and then its conclusion
wrongly negated.

Example: (Denying the Premise Fallacy)

The senator will be reelected only if he opposes the new tax bill.
But he was defeated. So he must have supported the new tax bill.

The sentence "The senator will be reelected only if he opposes
the new tax bill" contains an embedded if-then statement: "If the
senator is reelected, then he opposes the new tax bill." (Remember:
"A only if B" is equivalent to "If A, then B.") This in turn can
be symbolized as R-->~T. The sentence "But the senator was
defeated" can be reworded as "He was not reelected," which in turn
can be symbolized as ~R. Finally, the sentence "He must have
supported the new tax bill" can be symbolized as T. Using
these symbols the argument can be diagrammed as follows:

R-->~T~RTherefore, T

[Note: Two negatives make a positive, so the conclusion ~(~T) was
reduced to T.] This diagram clearly shows that the argument is committing
the fallacy of denying the premise. An if-then statement
is made; its premise is negated; then its conclusion is negated.

Transitive Property

A-->BB-->CTherefore, A-->C

These arguments are rarely difficult, provided you step back and
take a bird's-eye view. It may be helpful to view this structure
as an inequality in mathematics. For example, 5 > 4 and 4 > 3, so
5 > 3.

Notice that the conclusion in the transitive property is also an
if-then statement. So we don't know that C is true unless
we know that A is true. However, if we add the premise "A is true"
to the diagram, then we can conclude that C is true:

A-->BB-->CATherefore, C

As you may have anticipated, the contrapositive can be generalized
to the transitive property:

A-->BB-->C~CTherefore, ~A

Example: (Transitive Property)

If you work hard, you will be successful in America. If you are
successful in America, you can lead a life of leisure. So if you
work hard in America, you can live a life of leisure.

Let W stand for "you work hard," S stand for "you will be successful
in America," and L stand for "you can lead a life of leisure." Now
the first sentence translates as W-->S, the second sentence as S-->L,
and the conclusion as W-->L. Combining these symbol statements yields
the following diagram:

W-->SS-->LTherefore, W-->L

The diagram clearly displays the transitive property.

DeMorgan's Laws

~(A & B) = ~A or ~B~(A or B) = ~A & ~B

If you have taken a course in logic, you are probably familiar
with these formulas. Their validity is intuitively clear: The conjunction
A&B is false when either, or both, of its parts are false.
This is precisely what ~A or ~B says. And the disjunction
A or B is false only when both A and B are false, which is
precisely what ~A and ~B says.

You will rarely get an argument whose main structure is based on
these rules--they are too mechanical. Nevertheless, DeMorgan's laws
often help simplify, clarify, or transform parts of an argument.
They are also useful with games.

Example: (DeMorgan's Law)

It is not the case that either Bill or Jane is going to the party.

This argument can be diagrammed as ~(B or J), which by the second
of DeMorgan's laws simplifies to (~B and ~J). This diagram tells
us that neither of them is going to the party.

A unless B~B-->A

"A unless B" is a rather complex structure. Though surprisingly
we use it with little thought or confusion in our day-to-day speech.

To see that "A unless B" is equivalent to "~B-->A," consider the
following situation:

Biff is at the beach unless it is raining.

Given this statement, we know that if it is not raining, then Biff
is at the beach. Now if we symbolize "Biff is at the beach" as B,
and "it is raining" as R, then the statement can be diagrammed as
~R-->B.

CLASSIFICATION

In Logic II, we studied deductive arguments. However, the bulk
of arguments on the LSAT are inductive. In this section we will
classify and study the major types of inductive arguments.

An argument is deductive if its conclusion necessarily follows
from its premises--otherwise it is inductive. In an inductive argument,
the author presents the premises as evidence or reasons for the
conclusion. The validity of the conclusion depends on how compelling
the premises are. Unlike deductive arguments, the conclusion of
an inductive argument is never certain. The truth of the conclusion
can range from highly likely to highly unlikely. In reasonable arguments,
the conclusion is likely. In fallacious arguments, it is improbable.
We will study both reasonable and fallacious arguments.

We will classify the three major types of inductive reasoning--generalization,
analogy, and causal--and their associated fallacies.

Generalization

Generalization and analogy, which we consider in the next section,
are the main tools by which we accumulate knowledge and analyze
our world. Many people define generalization as "inductive reasoning."
In colloquial speech, the phrase "to generalize" carries a negative
connotation. To argue by generalization, however, is neither inherently
good nor bad. The relative validity of a generalization depends
on both the context of the argument and the likelihood that its
conclusion is true. Polling organizations make predictions by generalizing
information from a small sample of the population, which hopefully
represents the general population. The soundness of their predictions
(arguments) depends on how representative the sample is and on its
size. Clearly, the less comprehensive a conclusion is the more likely
it is to be true.

Example:

During the late seventies when Japan was rapidly expanding its
share of the American auto market, GM surveyed owners of GM cars
and asked them whether they would be more willing to buy a large,
powerful car or a small, economical car. Seventy percent of those
who responded said that they would prefer a large car. On the basis
of this survey, GM decided to continue building large cars. Yet
during the '80s, GM lost even more of the market to the Japanese.

Which one of the following, if it were determined to be true, would
best explain this discrepancy.

(A) Only 10 percent of those who were polled replied.
(B) Ford which conducted a similar survey with similar results continued
to build large cars and also lost more of their market to the Japanese.
(C) The surveyed owners who preferred big cars also preferred big
homes.
(D) GM determined that it would be more profitable to make big cars.
(E) Eighty percent of the owners who wanted big cars and only 40
percent of the owners who wanted small cars replied to the survey.

The argument generalizes from the survey to the general car-buying
population, so the reliability of the projection depends on how
representative the sample is. At first glance, choice (A) seems
rather good, because 10 percent does not seem large enough. However,
political opinion polls are typically based on only .001 percent
of the population. More importantly, we don't know what percentage
of GM car owners received the survey. Choice (B) simply states that
Ford made the same mistake that GM did. Choice (C) is irrelevant.
Choice (D), rather than explaining the discrepancy, gives even more
reason for GM to continue making large cars. Finally, choice (E)
points out that part of the survey did not represent the entire
public, so (E) is the answer.

Analogy

To argue by analogy is to claim that because two things are similar
in some respects, they will be similar in others. Medical experimentation
on animals is predicated on such reasoning. The argument goes like
this: the metabolism of pigs, for example, is similar to that of
humans, and high doses of saccharine cause cancer in pigs. Therefore,
high doses of saccharine probably cause cancer in humans.

Clearly, the greater the similarity between the two things being
compared the stronger the argument will be. Also the less ambitious
the conclusion the stronger the argument will be. The argument above
would be strengthened by changing "probably" to "may." It can be
weakened by pointing out the dissimilarities between pigs and people.

Example:

Just as the fishing line becomes too taut, so too the trials and
tribulations of life in the city can become so stressful that one's
mind can snap.

Which one of the following most closely parallels the reasoning
used in the argument above?

(A) Just as the bow may be drawn too taut, so too may one's life
be wasted pursuing self-gratification.
(B) Just as a gambler's fortunes change unpredictably, so too do
one's career opportunities come unexpectedly.
(C) Just as a plant can be killed by over watering it, so too can
drinking too much water lead to lethargy.
(D) Just as the engine may race too quickly, so too may life in
the fast lane lead to an early death.
(E) Just as an actor may become stressed before a performance, so
too may dwelling on the negative cause depression.

The argument compares the tautness in a fishing line to the stress
of city life; it then concludes that the mind can snap just as the
fishing line can. So we are looking for an answer-choice that compares
two things and draws a conclusion based on their similarity. Notice
that we are looking for an argument that uses similar reasoning,
but not necessarily similar concepts. In fact, an answer-choice
that mentions either tautness or stress will probably be a same-language
trap.

Choice (A) uses the same-language trap--notice "too taut." The
analogy between a taut bow and self-gratification is weak, if existent.
Choice (B) offers a good analogy but no conclusion. Choice (C) offers
both a good analogy and a conclusion; however, the conclusion, "leads
to lethargy," understates the scope of what the analogy implies.
Choice (D) offers a strong analogy and a conclusion with the same
scope found in the original: "the engine blows, the person dies";
"the line snaps, the mind snaps." This is probably the best answer,
but still we should check every choice. The last choice, (E), uses
language from the original, "stressful," to make its weak analogy
more tempting. The best answer, therefore, is (D).

Causal Reasoning

Of the three types of inductive reasoning we will discuss, causal
reasoning is both the weakest and the most prone to fallacy. Nevertheless,
it is a useful and common method of thought.

To argue by causation is to claim that one thing causes another.
A causal argument can be either weak or strong depending on the
context. For example, to claim that you won the lottery because
you saw a shooting star the night before is clearly fallacious.
However, most people believe that smoking causes cancer because
cancer often strikes those with a history of cigarette use. Although
the connection between smoking and cancer is virtually certain,
as with all inductive arguments it can never be 100 percent certain.
Cigarette companies have claimed that there may be a genetic predisposition
in some people to both develop cancer and crave nicotine. Although
this claim is highly improbable, it is conceivable.

There are two common fallacies associated with causal reasoning:

1.Confusing Correlation with Causation.

To claim that A caused B merely because A occurred immediately
before B is clearly questionable. It may be only coincidental that
they occurred together, or something else may have caused them to
occur together. For example, the fact that insomnia and lack of
appetite often occur together does not mean that one necessarily
causes the other. They may both be symptoms of an underlying condition.

2. Confusing Necessary Conditions with Sufficient Conditions.

A is necessary for B means "B cannot occur without A." A is sufficient
for B means "A causes B to occur, but B can still occur without
A." For example, a small tax base is sufficient to cause a budget
deficit, but excessive spending can cause a deficit even with a
large tax base. A common fallacy is to assume that a necessary condition
is sufficient to cause a situation. For example, to win a modern
war it is necessary to have modern, high-tech equipment, but it
is not sufficient, as Iraq discovered in the Persian Gulf War.

SEVEN COMMON FALLACIES

Contradiction

A Contradiction is committed when two opposing statements are simultaneously
asserted. For example, saying "it is raining and it is not raining"
is a contradiction. Typically, however, the arguer obscures the
contradiction to the point that the argument can be quite compelling.
Take, for instance, the following argument:

"We cannot know anything, because we intuitively realize that our
thoughts are unreliable."

This argument has an air of reasonableness to it. But "intuitively
realize" means "to know." Thus the arguer is in essence saying that
we know that we don't know anything. This is self-contradictory.

Equivocation

Equivocation is the use of a word in more than one sense during
an argument. This technique is often used by politicians to leave
themselves an "out." If someone objects to a particular statement,
the politician can simply claim the other meaning.

Example:

Individual rights must be championed by the government. It is right
for one to believe in God. So government should promote the belief
in God.

In this argument, right is used ambiguously. In the phrase "individual
rights" it is used in the sense of a privilege, whereas in the second
sentence right is used to mean proper or moral. The questionable
conclusion is possible only if the arguer is allowed to play with
the meaning of the critical word right.

Circular Reasoning

Circular reasoning involves assuming as a premise that which you
are trying to prove. Intuitively, it may seem that no one would
fall for such an argument. However, the conclusion may appear to
state something additional, or the argument may be so long that
the reader may forget that the conclusion was stated as a premise.

Example:

The death penalty is appropriate for traitors because it is right
to execute those who betray their own country and thereby risk the
lives of millions.

This argument is circular because "right" means essentially the
same thing as "appropriate." In effect, the writer is saying that
the death penalty is appropriate because it is appropriate.

Shifting The Burden Of Proof

It is incumbent on the writer to provide evidence or support for
her position. To imply that a position is true merely because no
one has disproved it is to shift the burden of proof to others.

Example:

Since no one has been able to prove God's existence, there must
not be a God.

There are two major weaknesses in this argument. First, the fact
that God's existence has yet to be proven does not preclude any
future proof of existence. Second, if there is a God, one would
expect that his existence is independent of any proof by man.

Unwarranted Assumptions

The fallacy of unwarranted assumption is committed when the conclusion
of an argument is based on a premise (implicit or explicit) that
is false or unwarranted. An assumption is unwarranted when it is
false--these premises are usually suppressed or vaguely written.
An assumption is also unwarranted when it is true but does not apply
in the given context--these premises are usually explicit.

Example: (False Dichotomy)

Either restrictions must be placed on freedom of speech or certain
subversive elements in society will use it to destroy this country.
Since to allow the latter to occur is unconscionable, we must restrict
freedom of speech.

The conclusion above is unsound because

(A) subversives do not in fact want to destroy the country
(B) the author places too much importance on the freedom of speech
(C) the author fails to consider an accommodation between the two
alternatives
(D) the meaning of "freedom of speech" has not been defined
(E) subversives are a true threat to our way of life

The arguer offers two options: either restrict freedom of speech,
or lose the country. He hopes the reader will assume that these
are the only options available. This is unwarranted. He does not
state how the so-called "subversive elements" would destroy the
country, nor for that matter, why they would want to destroy it.
There may be a third option that the author did not mention; namely,
that society may be able to tolerate the "subversives" and it may
even be improved by the diversity of opinion they offer. The answer
is (C).

Appeal To Authority

To appeal to authority is to cite an expert's opinion as support
for one's own opinion. This method of thought is not necessarily
fallacious. Clearly, the reasonableness of the argument depends
on the "expertise" of the person being cited and whether she is
an expert in a field relevant to the argument. Appealing to a doctor's
authority on a medical issue, for example, would be reasonable;
but if the issue is about dermatology and the doctor is an orthopedist,
then the argument would be questionable.

Personal Attack

In a personal attack (ad hominem), a person's character is challenged
instead of her opinions.

Example:

Politician: How can we trust my opponent to be true to the voters?
He isn't true to his wife!

This argument is weak because it attacks the opponent's character,
not his positions. Some people may consider fidelity a prerequisite
for public office. History, however, shows no correlation between
fidelity and great political leadership.